The Kingdom of Saudi Arabia, with its vast geographical area, and
its location at the boundary of the equatorial, has seen recently several
outbreaks of either tropical or Neglected Tropical Diseases (NTD).
Being the center of the Islamic world, with millions of pilgrimages
visiting the holy sites in Saudi Arabia in the annual sessions of
pilgrimage and Umrah, puts the world health at risk of wide and
uncontrolled epidemics with its close boundaries with both Yemen
and Egypt, which are the most countries in the Middle East region
harboring NTD’s, puts the Kingdom at an additional risk together
with the greenhouse effect of global warming and climate changes.
The current status of the NTDs in Saudi Arabia is currently unknown
due to several factors of which, poor reporting, lack of proper health
workers training and surveillance efforts, being the most important
factors. This mini-review will summarize the types of NTD’s diseases
and current status in Saudi Arabia.

Introduction

Diseases unique to the tropical and subtropical regions
(tropical diseases) are defined as Tropical medicine or
International Medicine. More recently the term Neglected Tropical
Diseases (NTD) has been introduced through the initiative of
the World Health Organization [1]. NTD’s (about 17 diseases)
are mostly infectious in nature and requires a vector for their
propagation, and are prevalent in the tropical and subtropical
regions, they were endemic even in countries with cold climates;
however with improvement with sanitation, heath education
and personal hygiene [2], in addition to the cold session, which
in part force the vector to hibernation, those diseases have been
eliminated or controlled.

NTD’s has a heavy burden on public health as they promote
poverty, reduced population production, child health, pregnancy
and health cost. Each NTD has its own unique etiological features,
geographic distribution and public health burden [3,4].

The most common vector for NTD’s transmission is insects
(mosquitoes and flies), which may carry a parasite, bacterium
or virus that is infectious to humans and animals and may act
as a biological reservoir for the pathogen multiplication and/
or incubator. In common, diseases transmission is caused by an
insect “bite”, through subcutaneous blood exchange [5].

Recent climate changes, also known as greenhouse effect,
in addition to, deforestation, rising immigration and increased international air travel and other tourism to tropical regions
has contributed to an increased incidence of NTD’s, which is can
cause high incidence of morbidity and mortality [6,7].

The localization of tropical diseases is in poor, underdeveloped
countries spanning the tropics, mainly in Africa, Asia, Central
America and South America, has led several international efforts
to combat those array of devastating diseases. The financial
burdens of those diseases are substantial [2,8].

While much of the current international efforts have been
focused on four diseases, namely Tuberculosis, Malaria, HIV and
Viral hepatitis, much less efforts or research has been geared
toward other NTD’s. Currently, more than a billion individual
is infected globally with NTD’s, including 500 million children
according to the latest WHO estimate [8].

The Kingdom of Saudi Arabia with its vast borders, and
especially its southern borders with close proximity to the
African horn and South East Asia, in addition to its subtropical
climates, puts the kingdom at risk for an epidemic or endemic
episodes of NTD’s.

According to recent estimates, the kingdom ranks the highest
second country in the Middle East North Africa (MENA) region
for Leishmaniasis (L. major) infection, with more than 4,000
reported cases; and the third country for Hookworm infection in
the region, with 0.4 million reported cases. Lymphatic filariasis
also has been reported in Saudi Arabia [9]. Accurate estimates
of the NTD’s cases in Saudi Arabia are often unavailable, due to
health system infrastructure, inefficient reporting system, beside
other factors [9].

Onchocerciasis

It is the world’s second leading infectious cause of blindness.
It is caused by Onchocerca parasitic worm. It is mode of
transmission is through black fly. Infection usually spread very
rapidly in patients leading to an immune response and destruction
of tissue, especially the eye. The prevalence in the Kingdom is
currently unknown. Another form of Onchocerciasis, known as
Aswad with severe dermatitis and edema is well documented in
Yemen; however information about its prevalence in the kingdom
is also lacking [10,11].

Leishmaniasis

Both cutaneous and visceral Leishmaniasis occurs in Saudi Arabia. The cutaneous type is common throughout the kingdom
especially in Eastern and Central provinces [12]. The visceral type
which is more virulent is confined to the South and Southwest
provinces. Dogs have been identified as the animal reservoir;
however, accurate information on the national prevalence of
the disease is not known [13]. Several studies have indicated the
presence of several hot areas of the diseases in different parts of
the country [12,13].

Toxoplasmosis

(Cat disease) is another important protozoan infection
thought to be present throughout the kingdom, with unknown
national prevalence [14]. Recent study reported that the
seropositivity of 487 pregnant women for Toxoplasma gondii
infection as high as 38.8% in the south western region of Saudi
Arabia [14]. Toxoplasmosis infection was also reported in other
regions of the country [15-17]. Toxoplasmosis infection is also
reported to be widely spread between animal species in Riyadh
region [18]. Toxoplasmosis is currently considered as a global
health threat as it infects 40-50% of the world population [19].

Brucellosis

It is a major health concern in Saudi Arabia. Its high
prevalence has been largely attributed to the social norms of the
nomadic population who live in close proximity with livestock
and consume raw milk, additionally, associated breakdowns
in veterinary health control systems and unrestricted animal
transportation through open borders have promoted the reemergence
of brucellosis in the Kingdom [20,21]. National
prevalence of the infection spread is currently unknown [9].

Dengue Virus (DENV)

A mosquito's transmitted disease is endemic in the western
and southern regions of the Kingdom, with outbreaks occurring
in 2006 and 2008. Recent studies indicated the persistent
endemic in the southern and western regions [22,23]. Three
strains of the 4 DENV strains were reported in the region and also
in neighboring Yemen [24]. Climate changes, increasing work
force from DENV endemic areas, plus increased urbanization will
eventually leads to increased risks of future outbreaks.

Rift Valley fever (RVF)

It is also a mosquito’s transmitted disease caused an outbreak
in 2000 in the Jazan region and other parts of the Kingdom [25].
This was the first recorded outbreak outside of Africa, affecting
several thousand animals and resulting in approximately 1,000
positive cases and several hundred deaths [26]. Public health
measure untaken to combat the spread of the disease seems to be
working and should be maintained [27].

Alkhurma Hemorrhagic Fever (AHFV)

It is caused by a tick-borne flavivirus, has also emerged on the
Kingdom in the Najran region in 1996. The knowledge gaps about
those viruses are still wide [28]. Recent reports indicate that the
epidemiology of the diseases is spreading among the population
and is moving outside its geographic areas [29].

Trypanosomiasis

Prevalence of African Trypanosomiasis infection in
humans, which is a parasitic disease, caused by protozoa called
trypanosomes and transmitted by the tsetse fly, is unknown in
the Kingdom [9]. Increased prevalence in animals and livestock
was noted in many animal species including camels, sheep and
cattle’s. Jazan region showed the highest level of infection rate
of camels of 40% with new species identified for the first time in
the country [30].

Lymphatic filariasis

It is well documented in Yemen, is a parasitic disease caused
by parasitic filarial worms transmitted by mosquitoes. Loa loa is
another filarial parasite transmitted by the deer fly. However, the
prevalence in the Kingdom is unknown.

Malaria

It has been documented as a major health problem in
several regions of the Kingdom. Malaria is caused by a Protozoan
parasites transmitted by female Anopheles mosquitoes. The
population at risk of malaria in the Kingdom is estimated to be 1.4
million and malaria epidemics frequently occur after heavy rains
sessions. On other hand, the existence of malaria in Southwestern
region of the Kingdom is greatly affected by the active and
continues importation of cases and vectors from Yemen. Malaria
vector control has been the focal aim for the health authorities,
Agriculture and local authorities. With the emergence of drug
resistant strains, the efforts should be maximized.

Both intestinal and urinary Schistosomiasis has been prevalent
in Saudi Arabia. Schistosomiasis is a parasitic disease caused by
several species of flatworm. Despite rigorous combating efforts
of the diseases in the kingdom, the current prevalence and hot
areas of the disease is unknown.

Tuberculosis (TB)

It is a bacterial infection of the lungs or other tissues, which
is highly prevalent in the world, with mortality rate of over
50% if untreated. It is a communicable disease, transmitted by
aerosol expectorant from a cough, sneeze, speak, kiss, or spit.
Over one-third of the world’s population has been infected by the
TB bacterium. The situation of TB in Saudi Arabia is unique. The
country has interesting and special population dynamics. There
are up to ten million expatriates mainly from endemic regions, in
South and South East Asia and over two million pilgrims visiting
the holy cities located in the western region of the Kingdom each
year, with the majority of pilgrims coming from endemic areas.
The current status of TB in the kingdom is unknown, especially
the new drug resistant strains.

While medical therapeutics and vaccines are the first line
of defense against tropical diseases, and despite the success of
vaccine development and manufacturing globally in combating
many diseases and alleviating the socioeconomic burden of those
diseases on public health, the need for more vaccine research
and development in tropical medicine is at its beak currently,
as evident by the race to develop an HIV, Hepatitis C or Malaria
vaccines are underway.

While vaccine development is a highly complex and lengthy
process as it may take from 10 to 12 years, and involve multiple
stages. The first stage involves the isolation of the pathogen
including all of its variants, and identifies the antigens. The
second stage is a preclinical
stage which begins with antigen
characterization and purification to develop appropriate vaccine
candidates. Animal studies are used to determine the immunogenicity
and safety of the candidate’s vaccine.

Another area of concern is the lack of rapid diagnostic devices
to screen large number of patients rapidly and cost effectively
with superior analytical and clinical sensitivity and specificity in
case of sudden outbreaks.

Tropical disease research is lacking in the Kingdom and the
region in general, where approximately more than 90% of human
and veterinary medicine or vaccines are imported, which poses
a serious public health burden and threat. Depending on foreign
suppliers is plagued by many risks of sudden outbreak, faulty
manufacturing, and surge in demands globally or market shift.
The Kingdom is in perfect position to lead international efforts
on tropical diseases research.